Variable resistance



Patented Dec. 27, 1927.

UNITED STATES *ERWIN R. STOEKLE, F MILWAUKEE, WISCONSIN.

VARIABLE RESISTANCE.

. Application field April 24, 1923. Serial No. 634,297.

- This invention relates to improvements in electrical resistances, particularly of the i type employing a resistor that would easily be injured by the usual methods of making a sliding or rubbing contact therewith. In my Patent #1,488,681, dated March 13th, 1923, and in my co-pending application, Serial No, 621,812, filed February 28th, 1923, electrical resistances are described in which the resistance is varied by pressing a metallic contact member into variable contact with the surface of a resistor. The absence of a sliding or rubbing motion of the contact member upon the resistor obviates any abrasion of the resistor which would result from theus'ual sliding contact. My present application describes new. and improved means for effecting a non-rubbing contact between the metallic contact member and the resistor.

@ne object of my present invention is to provide improved andsimplified means for pressing a contact member into controllably variable and intimate contact with a resis tor whereby the resistance between the ter- 1111118118 connected to said res1stor may be continuously and smoothly varied.

Another, object is to prdvide an improved form ofthis resistance particularly adapted to be; used as a so-called potentiometer resistance in which the resistance between the contact element and the end terminals of the resistor may be controllably varied.

Another object is to provide an improved form of this resistance in which the curve oi variation of the resistancc w'ith respect to displacement of the operating knob may be made of any desired form;

Another object is to provide a novel construction for accomplishing the above desired results in which the path of thecur rent shall be through a small thickness and relatively large area of the resistor there--.

i by permitting the use of a resistor circletively ,high specific resistance.

Other objects and novel features of this invention will be apparent from the following description and the accompanying drawings, Figures 1 to 5.

Figures 1 and 2 show a cross section and plan view respectively of a construction of the device in which the contact member con- .between terminal sists of a loose disc which may be inclined into contact with the resistor at a variable location thereon.v

Figure 3 shows a cross section of a construction in which the contact member is in the. form of a curved rocker whose tangency withthe resistor may be changed by means of a screw.

Figures 4 and 5 show two forms of the resistor element and its mounting particularly adapted to the construction of Figure 3.

Referring to Figure 1, the insulating base i has mounted upon it the resistor 2, which 1s connected at its ends. to the terminals 3 and 4:, shown in Figure 2. The contact disc 5 passes loosely over the shaft (Band rests upon the shoulder 7 on the threaded mountmg bushing 8. The shaft 6 has fzfstened to it the hub 9 which carries the spring pressure arm 10. The knob l1v serves to rotate the shaft 6 and its associated spring arm. The panel for mounting the device is shown at 12. A metallic connecting strip 13 connects the disc contact member 5 to the terminal 1a. A. pin 15 passes through a hole in the disc 5 and prevents a sliding motion of the disc upon the resistor as well as serving as a stop to limit the rotationof the arm 10.

, The disk 5 for an appreciable distance inwardly of its outer edge is pressed upwardly, as shown in the drawings, .to provide a smooth, conical contacting'surface adjacent the resistor 2, so that as the arm 10 is revolved over said disk, the said conical surface thereof is rolled over the resistor in tangential engagement therewith, thus varying the resistance in infinitesimal steps,

The operation of the device is as follows Current entering at either terminal 3 or 4.- passes through the resistor to the place where the disc 5 is pressedinto contact with the resistor by thespring arm 10. At this place the current enters the .disc passes through the connecting strip 13 and out at terminal 14. Rotationof the spring arm 10 location of the contact of the disc 5 upon the resistor and thereby Varies the resistance '14 and the terminals 3 and 4. v

Referring to the Figures 3 and 4;, the insulating base ,16 has mounted upon it the resistor strip 17 which is clamped thereto at its ends by the electrical terminals 18 and 19. The metal plates 20 and 21 extend under and make contact with the lower surface of the resistor strip over an area whose boundaries are shown by the dotted lines in Figure 4, Holes 22 and 23 are cut in both the metal plates and in the resistor to insulate these elements from electrical contact with the r threaded shaft 24 and the screw 25.

The curved contact member 26 is held in tangent relation to the resistor by means of the pressure sprin 27, the threaded shaft 24 and its co-operatmg nut 28. The shaft 24 passes freely throu h the mounting bushing 29 and through a s otted hole in the member 26 and may be rotated by means of the operating knob 30. The nut 28 fits in a recess on the upper edge of member 26 thus reventing its rotation. The screw is t eaded to the base and passes freely through the washer 31. Connections to the contact member are made at the terminal nuts 32 rotation reverses the above described variations. A resistance of relatively low value is attained when the contact of member 26 is directly over the lates 20 or 21 since in this case the path of t e current will be from the plate through the thickness of the resistor strip-only.

When it is desired to construct a rheostat of this type which shall'have a relatively low resistance the plates which. .make, contact withthe under surface of the resistor may have the form and extent indicated by the dotted lines in Figure 5. In this "construction the current entering at terminal 34 flows from the plate 35 substantially normal to'the plane of the resistor to the curved contact arm, thence back through the thickness of the resistor to the plate 36 and leaves at the terminal 37. A change in the location of tangency of the contact member upon the resistor changes the relative areas of contgct and therefore the relative resistances of t c paths of the current from thecontact member to the respective plates 35 and 36.

In the above described constructions any desired curve of variation of the resistance with respect to displacement of the operating knob may be obtained by cutting either the resistor strip or the underlying metal plates of the desired shape. It is apparent that when the plates are cut diagonally as shown in Figure 5 the resistance between terminals 34 and 37 remains substantially fixed irrespective of the position of the contact member. The resistance between the contact member and terminal 34 however decreases as the contact moves toward 34, whereas for the same movement the resistance between the contact member and terminal 37 increases at the same rate so that the resistance between terminals 34 and 37 remains substantially constant. This construction therefore permits of dividing the potential applied between the terminals 34 and 37 into proportionate parts which may be taken off between the contact member terminal and either of the endter'minals.

It will beobserved from the foregoing,

that I have provided a curved contact surface engaging a flat resistor in a line extending transversely over the entire exposed conducting surface of the resistor. In Fi ures 1 and 2 of the drawings, this is accomplished by turning up the marginal edge or surface of the disk to form a conically curved surfacewhich makes true linear tangency with the fiat resistor and rolls without sliding upon the surface of the resistor as the pressure arm is rotated. In Figure 3 of the drawings, wherein a linearly disposed resistor is employed in lieu of the circularly disposed resistor of Figure 1, the contact mem,-. ber also has a curved surface making a linear tangency with the surface of the flat resistor and isadapted to rock or roll upon said surface.

It will beobvious to those skilled in the art that the invention is susceptible of various changes and modifications without departing from the s irit thereof and it is not, therefore, desire to limit or restrict the same, except where limitations appear in the appended claims. A a I I What I claim as new and desire to secure by Letters Patent is 1. .An electrical resistance comprising an insulating base; a circularly disposed resistor in the form of a flat open ring mounted on the face of said base; suitable terminals for establishing electrical connections with said resistor; a disc shaped contact member placed substantially concentric with respect to said resistor, and having a circumferential conical surface extending adjacent the surface of saidresistor; means for preventing a sliding motion of said contact member upon said resistor, and means for inclining the plane of said contact member about a substantially centrally located point, whereby said contact member ma be brought into contact with said resistor .a variable loca-- tion along the latter, tus controllably changing the resistance between said contact member and either of the terminals of said resistor.

.2. An electric resistance unit comprising a substantially flat resistor having a smooth face of'conducting material, terminals therefor, a metallic contact element having a curved surface on one face thereof, said curved surface having transversely extending portions of substantial extent adjacent to and adapted to be engaged with said resistor, and means for rocking said element to effect contact thereof with said resistor at a variable location along the latter.

- 3'. An electrical resistance unit comprising a substantially fiat resistor having a smooth electrically conducting surface; terminals for said resistor; a contact element having a curved surface on one face thereof adjacent said conducting surface; said curved surface having transversely extending portions of substantial extent adapted to be engaged with said conducting surface; and means for rocking said contact element into a continuously variable location of contact along said conducting surface to effect a variation of resistance in infinitesimal steps.

4:. An electrical resistance unit comprising an insulating base, a flat resistor secured to said base and having a smooth conducting surface; suitable terminals for said resistor; a contact member having a curved surface on one face thereof, adjacent said conducting surface; said curved surface having transversely extending portions of substantial extent adapted to be engaged with saidconducting surface; means for preventing a sliding motion of said contact member on said conducting surface, and means for pressing said rolling contact member into firm contact with said conducting surface at a gradually variable location on said conducting surface, whereby the resistance between said contact member and either of said terminals may be varied in infinitesimal steps. I

5. A variable electrical resistance unit comprising an insulating base, a resistance element circularly disposed upon said base, said I element having a smooth electrically conducting surface; a disc shaped contact member having a substantial surface of one face and adjacent its periphery adapted to be pressed against said conducting surface; said surface of said disc-shaped contact member having transversely extending portions, of substantial extent engageable with said conducting surface; means for preventing a sliding motion of said peripheral surface upon said conducting surface; suitable termi- @jals for establishing electrical connections to said contact member and to said resistance element; and means including a rotatable spring pressure arm for pressing'said peripheral surface into substantially linear tangency with said conductiiig surface at a veriable location on the latter; whereby a substantial area of contact between said peripheral surface and said conducting surface is secured; and whereby a variation of resistance between said terminalsmay be accomplished in infinitesimal steps.

6. A variable electrical resistance unit comprising an insulating base; a resistance element circularly disposed upon said base; said element having a smooth electrically conducting surface; a contactmember having a conical surface adjacent said conducting surface 'of said resistance element, suitable terminals for establishing electrical connections to said contact member and to said resistance elements; means for preventing translation of said conical surface with respect to' said conducting surface; and means for. effecting a rolling tangential engagement of said conical surface upon said conducting surface whereby the resistance between said terminals may be varied in infinitesimal. steps. I 7. A variable electrical resistance unit comprising an insulating base, a resistance element mounted upon said base, said resistance element having a smooth fiat electrically conducting surface; a disc-shaped rigid contact member having a smooth conical surface near its circumference, said conical surface being adjacent said conducting surface; means for preventing rotation of said contact member; an element connecting said contact member to a terminal; suitable terminals for making electrical connections to the ends of said resistor; a spring pressure arm bearing upon said contact member and adapted to press said conical surface of-said contact member into firm contact with the conducting surface of said resistor;,a rotatable shaft fastened to said pressure arm and passing substantially through the vertex of the'coni- 'cal surface of said contact member; whereby rotation of said pressure arm by means of said shaftwill cause said conical, surface of said contact member to roll in a variable location of contact upon said smooth conducting surface of said resistor, thus permitting variation of resistance in infinitesimal steps between the terminal connected to said contact member and the terminals at the ends ofsaid resistor. 5 g

8. A contactfmember of the character described comprising a disc having its marginal edge upturned to form a conical contacting surface, and means for mounting said disc lid ing a disc having .a contacting surface of frustrated conical design adapted to have wabbling movement in operative posltion in. a rheostat.

10. An electrical resistance comprisingan motion to said contact member upon said 10 insulating base; a resistor mounted upon said resistor, whereby the location of tangency of base; suitable terminals for establishing said contact member upon said'resistor may electrical connections with said resistor; a be varied, and the resistance between said curved contact member having a convex contact member and either of said resistor surface adjacent the surface of said resistor terminals may be varied. 15 means for preventing asliding motion of said In Witness whereof, I have hereunto sub-' contact member upon said resistor; and con scribed my name.

'trollable means for imparting a rocking ERW'IN STOEKLE. 

